1. Field of the Invention
The present invention relates to an image forming apparatus and a paper feeding method which serve to correct a skew feed to a direction of delivery of a recording paper by a resist system.
2. Related Art
In an image forming apparatus using an electrophotographic process, a tip of a recording paper is aligned by means of a resist roller and the recording paper is then fed to transferring, separating and fixing portions. In this case, the resist roller matches the tip of the paper fed from a cassette or a tray by various separating methods with that of an image and corrects a oblique feed (skew) to a delivery direction. The correction is carried out in the following manner. Before the recording paper is fed to the transfer portion side for a next copy, a paper feed roller pushes the recording paper out of a cassette during a stop of the resist roller to cause a tip of the recording paper to abut on upper and lower contact portions (nip portions) of the resist roller, and furthermore, the recording paper is pushed against the abutting portion by means of the paper feed roller to correct a skew.
In the case of the resist system, the resist roller has the function of synchronizing a delivery speed of the recording paper with a circumferential speed of a photosensitive drum after correcting the skew. Therefore, a rotation is carried out in such a manner that a tip of an image is set in a timing with that of the recording paper, and an image is thus transferred onto the recording paper (for example, see JP-A-6-135589 Publication).
In the image forming apparatus using the resist system, there has been proposed a technique for operating an electromagnetic solenoid to rotate and drive a paper feed roller in order to decrease components of a mechanism for executing a paper feeding operation and an aligning operation of a paper, while bringing a resist clutch into a locking state to transmit a power to a resist roller, turning ON the electromagnetic solenoid again in a short time to unlock the resist clutch, thereby stopping the rotation of the resist roller temporarily when aligning the recording paper (for example, see JP-A-9-216754 Publication).
Furthermore, there has been known an image forming apparatus for turning ON a solenoid, thereby causing one of ends of a control member to enter a groove provided on a support member of a first planetary gear to control a rotation thereof and turning ON/OFF the solenoid, thereby causing the other end of the control member to enter a groove provided on a support member of a second planetary gear to control a rotation thereof (for example, see JP-A-9-211921 Publication). Any of developing sleeves for four colors is rotated.
The image forming apparatus described above (JP-A-6-135589 Publication) stabilizes a delivery and prevents a skew by using a rubber having a surface roughness capable of enhancing an adhesion of a recording paper and a roller in order not to cause the recording paper and the roller to slip. However, it is hard to maintain a high recording paper delivering property by only a material of the resist roller, and wrinkles, buckling and slips are generated on the recording paper.
Moreover, the image forming apparatus according to the (JP-A-9-216754 Publication) serves to decrease components for executing a paper feeding operation and a paper aligning operation and to temporarily stop the rotation of the resist roller. With the structure, even if the number of the components is decreased, an amount of flexure of the recording paper in a nip portion of the resist roller is not constant and wrinkles, buckling and slips cannot be prevented from being generated on the recording paper.
Similarly, the image forming apparatus (JP-A-9-211921 Publication) serves to rotate each developing sleeve of a developing device using a tandem method by utilizing an ON/OFF operation of a solenoid and normal and reverse rotations of a motor in order to form a visible image through toners having four colors of yellow (Y), magenta (M), cyan (C) and black (K). In the same manner as in the (JP-A-9-216754 Publication), wrinkles, buckling and slips of the recording paper cannot be prevented and an excellent recording paper delivering property cannot be maintained.